Formation of γ-alumina nanorods in presence of alanine

Article abstract of DOI:10.1016/j.materresbull.2010.10.011

Boehmite and alumina nanostructures were prepared using a simple green sol-gel process in the presence of alanine in water medium at room temperature. The uncalcined (dried at 200 °C) and the calcined materials (at 500, 600 and 700 °C for 4 h) were charac

Full text of DOI:10.1016/j.materresbull.2010.10.011

Materials Research Bulletin 46 (2011) 271–277
Contents lists available at ScienceDirect
Materials Research Bulletin
journal homepage: www.elsevier.com/locate/matresbu
Formation of
g-alumina nanorods in presence of alanine
a
b
Hossein A. Dabbagh a, , Elham Rasti , Mohammad S. Yalfani , Francesc Medina
*
b,**
a Catalysis Research Laboratory, Department of Chemistry, Isfahan University of Technology, 8415483111 Isfahan, Iran
b Departament d’Enginyeria Quı´mica, Universitat Rovira i Virgili, Av. Paı¨sos Catalans 26, 43007 Tarragona, Spain
A R T I C L E I N F O
A B S T R A C T
Article history:
Boehmite and alumina nanostructures were prepared using a simple green sol–gel process in the
presence of alanine in water medium at room temperature. The uncalcined (dried at 200 8C) and the
calcined materials (at 500, 600 and 700 8C for 4 h) were characterized using XRD, TEM, SEM, N2
physisorption and TGA. Nanorod aluminas with a possible hexagonal symmetry, high surface area and
relatively narrow pore size distribution were obtained. The surface area was enhanced and crystallization
was retarded as the alanine content increased. The morphologies of the nanoparticles and nanorods were
revealed by a transmission electron microscope (TEM).
Received 11 May 2010
Received in revised form 29 September 2010
Accepted 22 October 2010
Available online 29 October 2010
Keywords:
A. Oxides
ß 2010 Elsevier Ltd. All rights reserved.
A. Nanostructure
B. Sol–gel chemistry
C. X-ray diffraction
C. Electron microscopy
1. Introduction
found applications in industry as adsorbents, catalysts and catalyst
carriers, coatings and soft abrasives [10]. To prepare transition
Controllable pore size, narrow pore size distribution and
thermal and mechanical stability are interesting in many real
and potential applications that require molecular recognition, such
as shape selective catalysis, molecular sieving and selective
adsorption [1,2]. Several templating methods have been developed
to prepare large mesopore and macropore materials such as
polymer gels [3,4], emulsion [5,6], latex spheres [7] and even
bacteria [8] as templates. Ji et al. [9] synthesized microporous
alumina with a pore size <1.6 nm and a high surface area
(SBET = 674 m2/g) using aluminum tri-sec-butoxide precursor.
Alumina, one of the most studied ceramic materials, exists in
many metastable polymorphs as well as the thermodynamically
aluminas, the usual starting material is boehmite or pseudo
boehmite ( -AlOOH). Via calcination, the material passes through
the following series of phase transformations [11]:
Boehmite ! - ! - ! - ! -alumina
g
g
d
u
a
Zhang et al. [12] investigated the phase transformations upon
heat treatments and studied transition aluminas. Studies based on
the surfactant-assisted approach have involved different anionic
[13–15], cationic [13,16–19] and neutral [20,21] surfactants. Khalil
used cetyl trimethylammonium bromide (CTAB) as a cationic
surfactant and acetic acid as an organic modifier for the formation
of mesoporous alumina at room temperature [22]. Methods for
preparing ceramic fibers are melt spinning [23–26], melt extrac-
tion [27], pyrolysis of cured polymer fiber [28], unidirectional
freezing of gel [29,30] and sol–gel processing [31]. Anisotropic
nanostructures with controllable characteristics (phase, size,
shape and crystallinity) are hugely important due to their unique
properties and potentials, which are quite different from those of
the bulk counterparts [32,33]. Recently, much effort has been
stable
transition aluminas, can be divided into two broad categories: a
face-centered cubic arrangement of oxygen anions including -,
and -alumina, and a hexagonal close-packed arrangement of
oxygen anions consisting of - and -alumina. Thanks to their fine
particle size, their high surface area, and the catalytic activity of
their surface, transition aluminas (especially -alumina) have
a-alumina. Metastable alumina structures, also called
h
d-
u
k
x
g
focused on the preparation of boehmite (
because they can serve as catalyst supports [34], flame retardants
[35], and adsorbents [36], etc. So far, various anisotropic -AlOOH
g-AlOOH) nanomaterials
g
nanostructures have been prepared using solution-based synthetic
methods and usually including precipitation and hydrolysis.
Aluminum oxides are found in a wide range of polymorphs [37].
* Corresponding author. Tel.: +98 311 391 3257; fax: +98 311 391 2350.
** Corresponding author. Tel.: +34 977 559787; fax: +34 977 559621.
E-mail addresses: dabbagh@cc.iut.ac.ir (H.A. Dabbagh),
francesc.medina@urv.cat (F. Medina).
g
-Al2O3 is important in the fields of catalysis [38], ceramics [39],
0025-5408/$ – see front matter ß 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.materresbull.2010.10.011

272
H.A. Dabbagh et al. / Materials Research Bulletin 46 (2011) 271–277
adsorbents [40] and catalyst supports [41]. Wang et al. prepared
alumina nanofibers by hydrolyzing aluminum nitrate in the
presence of hexamethylenetetramine followed by the supercritical
fluid drying (SCFD) process [42].
2.3. Sample characterization
2.3.1. X-ray powder diffraction (XRD)
XRD measurements were acquired using a Bruker-AXS D8-
Discover diffractometer with a parallel incident beam (Go¨bel
mirror) and a vertical theta-theta goniometer, an XYZ motorized
stage mounted on an Eulerian cradle, diffracted-beam Soller slits, a
0.028 receiving slit and a scintillation counter as a detector. The
Recently, nanomaterials have received a considerable attention
because of their unique properties. Several techniques including
lithography, molecular beam epitaxy and chemical vapor deposition
have been used for the preparation of low-dimensional nanomater-
ials. However, the former technique has technological and economic
limits, especially in the case of fabricating ordered high-density
nanoarrays. Recently, the template-synthesis method (based on
orderedanodicaluminumoxide)hasattractedagreatattention[43].
Single-crystalline nanorods were synthesized by Zhu and coworkers
using thermal decomposition of boehmite precursor [44]. Zhu et al.
angular 2u diffraction range was between 5 and 808. The data were
collected with an angular step of 0.028 at 4 s per step and sample
rotation. Cuk radiation was obtained from a copper X-ray tube
˚
operated at 40 kV and 40 mA (l = 1.54 A).
2.3.2. Scanning electron microscopy (SEM)
synthesized
g
-alumina nanofibers from aluminum hydrate colloids
The SEM images were obtained with a JEOL JSM-6400 scanning
microscope operated at an acceleration voltage of 20 kV.
using poly(ethylene oxide) surfactant [45]. Kuiry et al. reported the
synthesis of boehmite nanofibers (the length of the boehmite
nanofibers was found to be more than 10
mm) by a modified sol–gel
2.3.3. Transmission electron microscopy (TEM)
process with aluminum isopropoxide precursor at room tempera-
ture [46]. Shen et al. developed a simple solid-phase method (using
steam-assisted wet-gel conversion process) for the synthesis of high
quality boehmite nanorods [47].
TEM images were acquired using a JEOL JEM-1011 microscope
operating at 80 kV. The samples were mounted on a carbon-coated
copper grid by placing a few droplets of a suspension of the ground
sample in acetone, followed by evaporation at ambient conditions.
Alumina nanorods have excellent high thermal stability and can
be extensively used as catalytic support in gas-gas separation and
petrochemical processing, especially in re-forming and isomeriza-
tion [48]. As a continuation of tubular nanostructural research
[49,50], and bearing in mind novel applications of alumina
nanostructures, in this article we report a process to synthesize
2.3.4. N2 physisorption
N2 physisorption was performed using a Micromeritics ASAP
2010 apparatus at 77 K. Before analysis, the samples were
degasified at 100 8C for 5 h. The BET method was applied to
calculate total surface area. The BJH model applied to the
desorption branch of the isotherm provides pore size distribution.
boehmite nanofibers and subsequently their transformation to g-
alumina nanorods via a simplified, green and less cumbersome
process. Addition of alanine would shape the size of the holes and
crevices. These changes should affect reactivity and/or selectivity
of the synthesized alumina (under investigation). We also study
the phase transformations of such boehmite powder to transition
aluminas and the effect of alanine on the morphology of the
aluminas. To our knowledge, this is the first report on the use of
this amino acid in the synthesis of templated alumina. The aim of
this report is to describe the synthesis of organized alumina
nanorods with a cheap source of aluminum and using an aqueous
medium with a novel structure-directing agent, alanine. This
compound belongs to the family of amino acids, which exist in
zwitterionic forms. Alanine mesocrystals obtained by stacking
nanocrystal platelets were recently described using a block
copolymer additive with an anionic polyelectrolyte block [51].
2.3.5. Thermal gravimetric analyses (TGA)
TGA analysis were performed by a Perkin Elmer TGA7 equipped
with a thermal analysis controller TCA 7/DX under a flow of
synthetic air and within a temperature range of 30–900 8C.
3. Results and discussion
3.1. X-ray powder diffraction
The XRD patterns of the gel powders made by drying the sol–gel
precursor at 200 8C are shown in Fig. 1. All peaks correspond to the
boehmite phase with an orthorhombic unit cell according to JCPDS
PDF No. 049-0133. However, a group of characteristic peaks for
alanine are observed when the Sn(alanine)/n(AIP) ratio was 1 [52].
2. Experimental
[)(TD$FIG]
2.1. Chemicals
∗
Aluminum isopropoxide (AIP), >98.0% (Merck), and alanine,
>99.0% (Merck), were purchased and used as received. In all
preparations distilled water was used as solvent.
∗
∗
2.2. Synthesis of g-AlOOH, g-and u-Al2O3
∗
∗
(c)
(b)
(a)
AIP (0.098 mol, 20 g) was dissolved in an excess of distilled water
(H2O/Al = 100) under vigorous stirring at 85 8C for 60 min. Alanine
was then added directly and refluxed for 24 h under stirring. The
molar ratios between alanine and aluminum (Sn(alanine)/n(AIP))
were: 0 (S0), 0.50 (S0.5)and1(S1). Thegel producedwas dried at70 8C
020
051
120
031
inanovenandthenheatedinairat200 8Ctoformg-AlOOH[S0 (200),
S0.5 (200) and S1 (200)]. The material obtained was named
uncalcined alumina. This was then calcined at 500, 600 and
700 8C for 4 h in static air with a heating ramp of 10 8C/min to yield
10
20
30
40
50
60
70
80
2θ (degree)
Fig. 1. XRD patterns of the boehmite powders: (a) S0 (200), (b) S0.5 (200) and (c) S1
(200) dried at 200 8C. (*) alanine and (ꢀ) boehmite.
different alumina phases (
(500), S0 (600), S0.5 (600), S1 (600), S0 (700), S0.5 (700) and S1 (700)].
g-, d- and u-Al2O3) [S0 (500), S0.5 (500), S1

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H.A. Dabbagh et al. / Materials Research Bulletin 46 (2011) 271–277
273
♦
correspond to
At a calcination temperature of 600 8C, the
coexist but -alumina is still the dominant phase (Fig. 2). When
g
-aluminas according to JCPDS PDF No. 050-0741.
d
- and -aluminas
g
♦
♦
♦
♦
g
♦
♦
♦
the thermal treatment temperature is increased further, the
diffraction peaks become slightly sharper and more peaks appear
for the samples calcined at 600 and 700 8C. All the diffraction peaks
exhibit high degree of broadness, which indicates the formation of
nanocrystals [12]. At a calcination temperature of 700 8C, for S0.5
♦
(g)
(f)
•
•
and S1, the g- and d- alumina were further converted to u-alumina
•
∗
∗
(JCPDS PDF No. 035-0121) (Fig. 2). However, with regard to Figs. 1
and 2, the 0 2 0, 1 2 0 and 0 5 1 peaks in dried gel at 200 8C and the
1 1 1, 4 0 0 and 4 4 0 peaks at 500 8C show a weaker intensity and
broadness when the amount of alanine increases. This indicates
that when the alanine/AIP ratio increases, more stabilized (less
crystalline) material (in terms of retardation of the crystallization)
is formed [22].
The temperature-dependent peak sharpening may be related to
crystal growth. The average crystallite size can be estimated by the
Scherrer formula [53]. The calculation was based on the diffraction
∗
∗
(e)
(d)
(c)
(b)
(a)
peak 0 2 0 centered on the 2
and the diffraction peaks centered on the 2
and -aluminas. S0 (200) and S1 (200) have average crystallite sizes
u
value of 148 for boehmite (at 200 8C)
u
value of 678 for the
g-
u
of 9.6 and 6.4 nm, and after calcination, the average crystallite sizes
of S0 (500), S0.5 (500) and S1 (500) are 7.8, 6.3, and 5.7 nm at 500 8C,
9.5, 9.6, and 8.3 nm at 600 8C and 11.1, 11.4, and 11.6 nm at 700 8C,
respectively.Thisshowsthatthehigherthecalcinationtemperature,
the larger the average crystallite size, a trend that is related to the
growth of the grain [12]. XRD patterns for the calcined material S0.5
and S1 at 500 8C show two main broad peaks, at d spacing values of
10
20
30
40
50
60
70
80
2 (degree)
θ
Fig. 2. XRD patterns of the samples: (a) S0.5 (500) b) S1 (500), (c) S0 (600), (d) S0.5
(600), (e) S1 (600), (f) S0.5 (700) and (g) S1 (700). Alumina phases are marked as: (^)
around 0.198 (2u = 468) and 0.141 nm (2u = 668), which are
u
-alumina, (*)
d
-alumina and (ꢀ)
g-alumina.
characteristic of weakly crystalline alumina (Fig. 2). However,
theintensityofthese peakswasweakand decreasedwhenthemolar
ratios for modified material were increased from 0.5 to 1.0 [22].
Only one diffraction peak of alanine (around 208) was detected for
the S0.5 (200) sample, which can be probably due to a well
dispersion of the alanine on the boehmite phase. The broad
diffraction lines of all the samples indicate the poor crystallinity of
the boehmite phase.
The XRD patterns of the calcined samples indicate that
transformations occurred from the boehmite phase to
-aluminas after calcination. The XRD patterns of the S0.5 and S1
3.2. N2 physisorption
The N2 adsorption/desorption isotherms of the samples are
shown in Fig. 3 (top). The isotherms of the samples at 200 and
500 8C are characterized as type IV with an H2 hysteresis loop that
is broad with a long and almost flat plateau and a steep desorption
branch. This type contains complex interconnected pores. Type IV
isotherm is a characteristic of mesoporous materials with a
hysteresis loop [54]. The hysteresis loops of nitrogen sorption
g-, d- and
u
samples calcined at 500 8C are shown in Fig. 2. At this temperature
no peaks related to alanine are observed, which indicates that
alanine was removed during calcination. All detected peaks
[()TD$FIG]
240
200
160
120
80
400
350
300
250
200
150
100
50
450
400
350
300
250
200
150
100
50
350
300
250
200
150
100
50
40
0
0
0
0
100 200 300 400 500 600 700
P/P
0
100 200 300 400 500 600 700
P/P
0
100 200 300 400 500 600 700
P/P
0
100 200 300 400 500 600 700
0.040
0.035
0.030
0.025
0.020
0.015
0.010
0.005
0.000
0.030
0.025
0.020
0.015
0.010
0.005
0.000
0.020
0.016
0.012
0.008
0.004
0.000
0.020
0.016
0.012
0.008
0.004
0.000
1
10
100
1
10
100
1
10
100
1
10
100
Pore size (nm)
Pore size (nm)
Pore size (nm)
Pore size (nm)
Fig. 3. Nitrogen adsorption/desorption isotherms for the as-prepared boehmite powder at (Sn) alanine/nAIP = 0, 0.5 and 1 dried at 200 8C and the samples calcined at 500 8C,
600 8C and 700 8C (top), and their BJH pore width distribution (bottom).

[
H.A. Dabbagh et al. / Materials Research Bulletin 46 (2011) 271–277
Fig. 4. TEM images of the sol–gel synthesized alumina materials. (A) S0 (200), (B) S1 (200), (C) S0 (500), (D) S1 (500), (E) S0 (700) and (F) S1 (700).
isotherms are typical for textural porosity [55]. For the samples
prepared in the presence of alanine and calcined at 200 and 500 8C,
the hysteresis loop is located at P/P0 ꢁ4.0–8.0. The hysteresis loop
is broader for the samples calcined at 500 8C, which indicates that
the samples are more porous. When the samples were calcined at
600 and 700 8C, they all showed type IV isotherms with H1
hysteresis loops. This is believed to occur with systems that have a
narrow distribution of uniform pores with a well-organized,
ordered porosity (Fig. 3 top) [56]. The shape of the hysteresis loops
can be correlated with the change in pore structure, which in this
case can be a phase transformation from boehmite to transition
alumina with different morphologies [12].
(342 m2/g) obtained by double hydrolysis method reported by Bai
et al. in which Pluronic P123 was used as structure directing agent
[57]. The average pore diameter for the samples calcined at 500 8C
is in the 4.7–7.4 nm range. Further increases in the calcination
temperature to 600 and 700 8C lead to a decrease in surface area
and an increase in the average pore diameter for all samples. Note
that the phase changes from
temperature range.
g-alumina to d- and u-alumina at this
A narrow mesopore size distribution (below 10 nm), on the
other hand, is especially interesting for both catalytic and
adsorption applications. It may lead, for instance, to the appear-
ance of electronic confinement effects, as suggested by Wang et al.
to explain the remarkable properties for the adsorption of metals
(particularly Zn) [18,58]. The higher porosity of S1 than that of S0
for the samples calcined at 500, 600 and 700 8C may be due to the
introduction of the surfactant (alanine) into the porous structure of
the samples. This can lead to a higher adsorption capacity of the
calcined samples. When boehmite is calcined at 500 8C, the alanine
is completely removed. Moreover, at this temperature, dehydrox-
ylation begins and hydrogen bonds are disintegrated, which leads
Table 1 lists the calculated BET specific surface area, the pore
volumes and the average pore diameters of the samples containing
different amounts of alanine calcined at temperatures between
200 and 700 8C. Specific surface areas of the samples SBET were
obtained within the 127–422 m2/g range. For the samples calcined
at 200 8C, as the mol ratio of alanine increased, the specific surface
area decreased. Here, some of the analine occupies the internal
spaces of the pores, a fact that is reinforced by a decrease in the
pore volume and diameter of the samples. Note that up to a
temperature of 500 8C, the calcination process increases the
surface area of the samples containing alanine. This increase in
surface areas is greater for the sample containing the largest
amount of alanine. The S1 (200) sample has a surface area of
242 m2/g, whereas the S1 (500) sample has a surface area of
to the formation of the spherical shaped
g-alumina with greater
specific surface area and pore volume up to meso-size. When the
calcination temperature is increased further, Ostwald ripening
may occur and the agglomerated crystallites are more densely
sintered, thus leading to the progressive reduction in specific
surface area and pore volume to meso-size. However, the S1
sample calcined at higher temperatures always has the highest
422 m2/g. This result is higher than the surface area of
g-alumina

H.A. Dabbagh et al. / Materials Research Bulletin 46 (2011) 271–277
275
Table 1
temperature increased. This increase must be due to the trapping
of alanine molecules inside holes and crevices. The high vapor
pressure of the decomposed alanine can also influence shape and
porosity. As the concentration of alanine increased, the crystallite
size of alumina decreased. Alanine molecules prevent the
interaction of small particles to form a larger one. The crystallite
size of the samples is one of the most important parameters to
influence the rate of transition of alumina. Therefore, if the
crystallite size is decreased in the presence of alanine, the rate of
Textural characteristics of the prepared samples.
Materials and calcination
SBET (m2/g)
Vp (cm3/g)
dp (nm)
S0 (200)
S0.5 (200)
S1 (200)
284
263
242
0.38
0.27
0.23
3.9
3.8
3.7
S0 (500)
S0.5 (500)
S1 (500)
278
325
422
0.42
0.50
0.59
7.4
5.1
4.7
transition of
g-alumina to u-alumina will increase. The pore
S0 (600)
S0.5 (600)
S1 (600)
180
208
210
0.41
0.46
0.52
10.1
9.3
diameters decreased from 3.9 to 3.7 nm, from 7.4 to 4.7 nm and
from 10.1 to 7.3 nm at 200, 500 and 600 8C, respectively, but
increased from 12.3 to 14.3 nm at 700 8C. These decreases are due
to a higher dehydration rate and the formation of smaller pores.
The increase may be due to the decomposition of unstable intra
and/or intermolecular crosslinks.
7.3
S0 (700)
S0.5 (700)
S1 (700)
127
129
193
0.38
0.42
0.50
12.3
12.8
14.3
Fig. 3 (bottom) shows the pore size distributions measured by
the Barrett-Joyner-Hatenda (BJH) model. It can be seen that the
pore sizes of the samples dried at 200 8C are in the 3.6–7.3 nm
range. For the calcined materials (at 500, 600 and 700 8C for 4 h)
they are in the 4.1–11.1 nm range. The increase in porosity at
higher calcination temperatures observed in S0.5 to S1, may be
associated with the presence of alanine. Moreover, the greater
adsorption capacity for the calcined S1 than for the S0.5 can be
explained by the increased porosity created by increasing the
alanine ratio during the preparation of the material.
surface area. These changes in surface area and pore size may be
related to the morphologies of the transition alumina nanos-
tructures, which are probably stabilized by the presence of alanine.
The surface areas of the synthesized
700 8C (422–127 m2/g) in this study are larger than those normally
observed for conventional
-alumina (255–189 m2/g) [59].
Two possible mechanisms for the synthesis of -alumina using
g- and u-alumina at 500–
g
g
alanine were suggested. First, the acidic proton may catalyze the
dehydration process. Second, the alumina hydroxyl that is a poor
leaving group requires a higher temperature to dehydrate. Adding
alanine converts the hydroxyl to a much better leaving group (ester
moiety), which in turn leaves at a lower temperature, thus
3.3. TEM and SEM
enhancing the formation of
g
-alumina. The pore volume of
TEM and SEM analyses were performed to evaluate the
morphologies and sizes of the synthesized samples. A worm-
alumina increased as the molar ratio of alanine and the
[()TD$FIG]
Fig. 5. SEM photographs of (A) as-dried boehmite S0 (200), (B) S0 (500), (C) S1 (200) and (D) S1 (500) powder.

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H.A. Dabbagh et al. / Materials Research Bulletin 46 (2011) 271–277
100
95
S0
S0.5
S1
90
85
80
75
70
65
60
0
200
400
600
800
T (oC)
Fig. 6. TGA-DTA curves of the uncalcined S0, S0.5 and S1 samples.
hole-like morphology was observed only for S0 (200) (Fig. 4A)
[60,61]. Individual nanorods could be distinguished when the S1
very minor weight loss in the TGA curve may be attributed to the
crystallization of transition alumina and/or the decomposition of
residual organics and the further continuation of the dehydrox-
ylation process [22]. No significant weight loss is observed above
600 8C. A total weight loss of ꢁ29.54% for S0.5 ad 35.18% for S1 is
observed during the decomposition process, which, as expected,
indicates a higher amount of analine in the S1 sample. The
decomposition temperature of free alanine is 295–297 8C [65]. TGA
curve for the sample without alanine (S0) showed one major
decomposition step at less than 100 8C due to the elimination of
water.
(200) sample was calcined at 500 8C and 700 8C and formed
g-
alumina and -alumina phases (Fig. 4D and F). The TEM images in
u
Fig. 4 show that the nanorods have a length of about 10 nm. The
TEM image of S1 (200) (Fig. 4B) shows almost the same
morphology as the samples calcined at 600 and 700 8C but as
intertwined particles, when the sample still contained alanine. The
solid transformation of boehmite to alumina is a classical example
of a topotactic reaction. The morphology of boehmite is therefore
preserved in the morphology of g-alumina [62]. The sizes of the S1
(700) nanorods are relatively similar. The nanorods of S1 (700) have
diameters from 6 to 8 nm and lengths of 17–18 nm. The SEM
images of the samples are given in Fig. 5. A general view on these
micrographs demonstrates spherical grains with close vicinity
which have been accumulated on each other. However for the S1
(500) sample made using alanine, after thermal treatment free
inter-grain spaces and porosity created in effect of alanine
elimination could be observed.
4. Conclusions
A green and facile procedure was introduced for the synthesis of
boehmite with an average crystallite size of 7 nm. After calcination,
nanorods g-Al2O3 with excellent porous characteristics (a specific
surface area of 422 m2/g and a pore volume of 0.59 cm3/g) were
obtained. This method can also be used to prepare mesoporous
alumina powders or conduct surface modification of other
3.4. Thermal gravimetric analyses
materials. In this work,
temperatures below those reported. At lower temperature, when
the alanine content was increased from 0.5 to 1 mol ratios, the g-
alumina had the smaller average crystallite size, while at 700 8C
the crystallite size was larger.
d- and u-alumina was obtained at
Fig. 6 shows the TGA-DTA curves for the uncalcined samples. In
light of the thermal analysis studies for similar alanine-containing
systems [63], two main decomposition steps are recognized. On
heating, amino acids behave like hydroxy acids and lose water
through condensation [64]. The thermograms of the samples
containing alanine show an initial stage of weight loss (from room
temperature to 150 8C), due to physically adsorbed water. The
second weight loss, between 200 and 510 8C, is ascribed to the
dehydroxylation process of boehmite and the removal of the
template (alanine) through a decomposition reaction. At 550 8C, a
Acknowledgements
We gratefully acknowledge support for this study from the
Isfahan University of Technology (IUT). We also acknowledge the
invaluable discussions of Dr. K. Shams of the Department of
Engineering at IUT.

H.A. Dabbagh et al. / Materials Research Bulletin 46 (2011) 271–277
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